Making microgels photo-responsive by complexation with a spiropyran surfactant

Area of Science:

• Polymer Science
• Materials Science
• Photochemistry

Background:

• Poly(N-isopropylacrylamide-co-acrylic acid) [p(NIPAM-AA)] microgels exhibit volume phase transitions.
• Spiropyran (SP) surfactants undergo light-induced isomerization, changing their charge and hydrophobicity.
• Anionic microgels can complex with cationic or charged surfactants.

Purpose of the Study:

• To investigate the photo-triggered responsiveness of p(NIPAM-AA) microgels complexed with spiropyran (SP) surfactants.
• To understand how light influences the microgel's size and volume phase transition temperature (VPTT).
• To explore the impact of surfactant properties and irradiation conditions on microgel behavior.

Main Methods:

• Complexation of anionic p(NIPAM-AA) microgels with SP-containing surfactants.
• Irradiation of microgel-surfactant complexes with UV and visible light.
• Characterization of microgel size and VPTT as a function of light wavelength, intensity, surfactant concentration, and microgel charge density.

Main Results:

• Complexation leads to charge compensation, reducing microgel size and lowering VPTT to 32 °C.
• Light irradiation isomerizes SP surfactant from charged merocyanine to a more hydrophobic form, causing reversible microgel size changes.
• Microgel size and VPTT modulation are influenced by light absorption-induced heating and changes in surfactant hydrophobicity.

Conclusions:

• SP-functionalized surfactants effectively trigger photo-responsiveness in p(NIPAM-AA) microgels.
• The reversible changes in microgel size and VPTT are controllable via light stimuli.
• This system offers potential for light-responsive materials and drug delivery applications.